What a Chicago winter does to a masonry chimney
No part of the country is gentler on a chimney than another, but Chicago is genuinely punishing in a specific way: water and cold working together. Through the burning season the brick gets soaked by snowmelt and the wind-driven rain off the lake, and then the temperature drops below freezing, sometimes many times in a single week. Any moisture sitting in the porous brick or the mortar joints expands as it freezes, prying the joint open a hair, then thaws and seeps deeper, then freezes again. Repeat that cycle across a hard Cook County winter and you get spalling brick faces, crumbling mortar, and a crown that has quietly cracked from end to end. The damage is slow and almost invisible from the ground, which is exactly why so much of it goes unaddressed until water is staining a bedroom ceiling.
Heavy use is the other half of the story here. Chicagoans actually burn through these winters, and a fireplace or a wood stove that runs night after night lays down creosote inside the flue faster than an occasional-use chimney ever would. Creosote is the tarry, combustible residue that condenses on the cool upper flue, and once it builds into a thick glaze it is both a chimney-fire hazard and a sign the flue is running cooler or dirtier than it should. The same hard-working chimney that keeps a bungalow warm in February is the one most likely to need a sweep and a careful camera look before the next heating season, and reading both the moisture damage and the creosote load is the heart of what we do.